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Fuel tank mystery: Here's what I found inside

Paparock1

Angry SE
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I wonder if someone hasnt replaced the fuel pump unit in the past with a fuel pump for a 19 gallon tank and put it in a 15 gallon tank. They are different. The fuel level float is the only diffence.

I also have a 97 SE. I did the fuel tank mod and now my fuel gauge reads full for 85 miles before it starts to show signs of usage. This is probably one of my favorit mods as it didnt cost anything and then I am not stopping at a gas station every other day. I also could not figure out why I could only put 10 gallons of gas in. I put a 5 gallon gas can in the back and drove until it was out of gas. My low fuel light comes on with 4 gallons of gas left in the tank. Now when I see my low fuel light come on I know I can safe go another 65 miles before running out.

I would bet that if you did the vent tube mod you could get 19 gallons in your tank and your gauge would then read full.

you only need to trim the vent tube. I left the filler tube alone, I liked the idea of the anti siphon hinderance to a would be theif.
 
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SSTJ

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I wonder if someone hasnt replaced the fuel pump unit in the past with a fuel pump for a 19 gallon tank and put it in a 15 gallon tank. They are different. The fuel level float is the only diffence.

I also have a 97 SE. I did the fuel tank mod and now my fuel gauge reads full for 85 miles before it starts to show signs of usage. This is probably one of my favorit mods as it didnt cost anything and then I am not stopping at a gas station every other day. I also could not figure out why I could only put 10 gallons of gas in. I put a 5 gallon gas can in the back and drove until it was out of gas. My low fuel light comes on with 4 gallons of gas left in the tank. Now when I see my low fuel light come on I know I can safe go another 65 miles before running out.

I would bet that if you did the vent tube mod you could get 19 gallons in your tank and your gauge would then read full.

you only need to trim the vent tube. I left the filler tube alone, I liked the idea of the anti siphon hinderance to a would be theif.

Yep, pretty much the same story for me, as in my link a few posts back. But I agree that in this case, it could also be the OP's sending unit or a faulty gauge.

Forgive me if I've already shared these, but as you have a 97 and an SE, check out the links in my signature and let us know if you have anything to add!
 
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Tim_with_the_tj

Tim_with_the_tj

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I have the same year same build year and same exact problem filling my tank. Only get about 9 gallons max. I’m about to pull the tank for the 2nd time, did you ever solve the problem?
I’ve been traveling so I haven’t fixed this yet. I will reply after I have time to drop the tank again. Currently it’s got half a tank and I don’t drive it much right now. Waiting for a new front driveshaft so it’s not seeing any off-road time at the moment. I barely drive it on the street.
 

Derweazel

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Gosh, I wish I'd seen this thread sooner. I had the same problem, and the solution is described here.

Short story: drop the tank again and trim back the vent tube, not the filler tube.

Edit: But be sure your gauge isn't off. I haven't read all the posts in this thread, but there is a chance that your gauge is just reading 3/4 when it's really full, and reading E when it's really 1/4. When the light comes on, you should have 3 gallons left (12 +3 = 15). I learned the hard way (got stranded) that my gauge was indeed correct, but my tank wouldn't let me fill past 3/4.
Thank you for the reply, that gives me a couple different things to look at when i drop it this time. I didnt see any pictures on your post that were referred to. Are the photos availible anwhere else online?
 

Derweazel

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I’ve been traveling so I haven’t fixed this yet. I will reply after I have time to drop the tank again. Currently it’s got half a tank and I don’t drive it much right now. Waiting for a new front driveshaft so it’s not seeing any off-road time at the moment. I barely drive it on the street.
Thats how mine is for the most part, short wheeling trips and not much town driving. However we have a desert trip coming up and would like to make sure i know how much fuel i have.
 
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SSTJ

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I’ve been traveling so I haven’t fixed this yet. I will reply after I have time to drop the tank again. Currently it’s got half a tank and I don’t drive it much right now. Waiting for a new front driveshaft so it’s not seeing any off-road time at the moment. I barely drive it on the street.

Oh, sorry, you PMed me about this right? Yes, I remember that you're traveling. Gotta learn to get my Avatars and screen-names straight. I thought this was yet another user with the same problem.
 
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SSTJ

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Thank you for the reply, that gives me a couple different things to look at when i drop it this time. I didnt see any pictures on your post that were referred to. Are the photos availible anwhere else online?

There are a few pics in the links in that post. But not many; maybe just one of the filler tube and vent tube before I cut the vent tube.
 
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Tim_with_the_tj

Tim_with_the_tj

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Oh, sorry, you PMed me about this right? Yes, I remember that you're traveling. Gotta learn to get my Avatars and screen-names straight. I thought this was yet another user with the same problem.
Yep, that was me you’ve been talking to through PMs. I plan to make the cut to the vent tube like you did, and effectively get a 19 gal tank out of it. I also ordered a new Delphi fuel pump assembly for 19 gal tank. I already have longer starting times when the Jeep sits for even just 15 mins so there’s a drain back issue. If I cycle the key a few times it fires up quicker. I figured if I’m dropping the tank again I might as well change all that. Then my fuel gauge will read correctly for the increased capacity afterwards as well.
 
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Tim_with_the_tj

Tim_with_the_tj

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I wonder if someone hasnt replaced the fuel pump unit in the past with a fuel pump for a 19 gallon tank and put it in a 15 gallon tank. They are different. The fuel level float is the only diffence.

I also have a 97 SE. I did the fuel tank mod and now my fuel gauge reads full for 85 miles before it starts to show signs of usage. This is probably one of my favorit mods as it didnt cost anything and then I am not stopping at a gas station every other day. I also could not figure out why I could only put 10 gallons of gas in. I put a 5 gallon gas can in the back and drove until it was out of gas. My low fuel light comes on with 4 gallons of gas left in the tank. Now when I see my low fuel light come on I know I can safe go another 65 miles before running out.

I would bet that if you did the vent tube mod you could get 19 gallons in your tank and your gauge would then read full.

you only need to trim the vent tube. I left the filler tube alone, I liked the idea of the anti siphon hinderance to a would be theif.
Well, it’s been a while but I finally made time to work on this. I’m gonna tag @SSTJ here because he was helping me out on this through PMs. Here’s how it all played out.

I ran the tank down to an uncomfortably low level on purpose beforehand. Here’s what the gauge read before I dropped the tank today.
5A6BE3D6-BEB0-423D-AC0D-59628B766C19.jpeg


And here’s how much fuel was left in the tank.



I’d say that’s about 4-4.5 gallons. The gauge was buried below the red, on E.

The fuel pump assembly I removed was identified as Airtex via a very faded sticker on the hat. It was still working, but I think the sending unit is toast judging by the way it looks and the amount of fuel I found in the tank. I would have expected less fuel remaining with that reading on the gauge.

C7A606B8-8E17-4C66-B28F-A68F6A7A7793.jpeg


The sliding electrical piece looks very worn. It was not making great contact as the float goes up and down. It looked loose and not sure if that could have contributed to a false reading on the gauge. I could only ever get the gauge to read about 3/4 full as well.

Now here’s the kicker. The new 19 gal Delphi pump assembly did not fit this tank. I read that it would fit. False. It was too tall and would not seat enough to seal correctly at the top of the tank.

Here’s a comparison of the height of the buckets/cages, whatever you call them.

26DD5B70-6302-4EEA-A16D-79AADEB341A7.jpeg

On the left is the new Delphi 19 gal and on the right is the Airtex (it’s leaning due to one missing rubber grommet on bottom).

Here is my tank part number. It’s the 15 gal tank, 1997 SE 4 cyl.
DD86388D-2AD6-4BDA-9D82-672CB317B12F.jpeg


After trying a few things to make the new Delphi 19 gal unit fit, I realized it was just too damn tall. I ended up deciding to Frankenstein the two units together. I wanted my Jeep in running order.

B3C01B8B-7D56-4D9A-8F94-BEED4803A567.jpeg

990781E1-C351-4AEF-BD16-F26A510AEE39.jpeg

Cut the cage to match the height of the one I removed. Not only was the cage too tall, but the new pump and hat assembly would not compress enough either. It was also too tall due to the use of a plastic tube with spring that attaches the pump to the hat. (Not shown)

24DD9F83-5DF7-4396-9A6F-7A7B75DA7634.png

The old hat uses a submerged fuel line to connect the pump. I installed the new pump into the old hat and switched out the wiring harnesses for the new ones. This setup will seat correctly in the tank.

Getting it all put back together I was able to use the new pump, new sending unit/float, and old hat with FPR.

A50E43EC-0A4C-488C-AEDB-D157FE432BDE.jpeg


While the tank was down I cut the vent tube to about 1 inch. Here’s the piece I cut off.

B689AB46-001C-40BC-8CED-9585E0BFCDED.jpeg


Once I got the tank back into the Jeep I added the fuel I previously removed plus another two gallons. So I’d say around 6-6.5 gallons total. Here’s what the gauge read.

8232B6FB-49ED-4EAA-B987-6B61D0C8332D.jpeg


It was late when I finished this so I haven’t been to the gas station yet. I will report back with how many gallons I’m able to get into the tank now.
 
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SSTJ

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Well, it’s been a while but I finally made time to work on this. I’m gonna tag @SSTJ here because he was helping me out on this through PMs. Here’s how it all played out.

I ran the tank down to an uncomfortably low level on purpose beforehand. Here’s what the gauge read before I dropped the tank today. View attachment 302466

And here’s how much fuel was left in the tank.

View attachment 302468

I’d say that’s about 4-4.5 gallons. The gauge was buried below the red, on E.

The fuel pump assembly I removed was identified as Airtex via a very faded sticker on the hat. It was still working, but I think the sending unit is toast judging by the amount of fuel I found in the tank. I would have expected less fuel remaining with that reading on the gauge.

View attachment 302464

The sliding electrical piece looks very worn. It was not making great contact as the float goes up and down. It looked loose and not sure if that could have contributed to a false reading on the gauge. I could only ever get the gauge to read about 3/4 full as well.

Now here’s the kicker. The new 19 gal Delphi pump assembly did not fit this tank. I read that it would fit. False. It was too tall and would not seat enough to seal correctly at the top of the tank.

Here’s a comparison of the height of the buckets/cages, whatever you call them.

View attachment 302470
On the left is the new Delphi 19 gal and on the right is the Airtex (it’s leaning due to one missing rubber grommet on bottom).

Here is my tank part number. It’s the 15 gal tank, 1997 SE 4 cyl.
View attachment 302473

After trying a few things to make the new Delphi 19 gal unit fit, I realized it was just too damn tall. I ended up deciding to Frankenstein the two units together. I wanted my Jeep in running order.

View attachment 302471
View attachment 302472
Cut the cage to match the height of the one I removed. Not only was the cage too tall, but the new pump and hat assembly would not compress enough either. It was also too tall due to the use of a plastic tube with spring that attaches the pump to the hat. (Not shown)

View attachment 302474
The old hat uses a submerged fuel line to connect the pump. I installed the new pump into the old hat and switched out the wiring harnesses for the new ones. This setup will seat correctly in the tank.

Getting it all put back together I was able to use the new pump, new sending unit/float, and old hat with FPR.

View attachment 302475

While the tank was down I cut the vent tube to about 1 inch. Here’s the piece I cut off.

View attachment 302477

Once I got the tank back into the Jeep I added the fuel I previously removed plus another two gallons. So I’d say around 6-6.5 gallons total. Here’s what the gauge read.

View attachment 302476

It was late when I finished this so I haven’t been to the gas station yet. I will report back with how many gallons I’m able to get into the tank now.

Wow, nice work! Yes, definitely sounds like your gauge (sending unit) was off. Fixing that might have been the only thing you needed, whereas in my case the gauge was accurate. But of course you should now also be able to get a total of 19 gallons in there, from trimming the vent tube.

Good job hacking that pump assembly. I would probably have chickened out at that point.

I'm surprised that the 19-gallon Delphi was a different size. I wonder if it was for a later-model TJ, which might have a differently-shaped tank?
 
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mrblaine

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I'm surprised that the 19-gallon Delphi was a different size.
Yeah, that is more than a bit odd.
I wonder if it was for a later-model TJ, which might have a differently-shaped tank?
Nope, all TJ tanks are the same shape and external size give or take a few sixteenths of an inch.

What does happen and I've seen this in person and reported on the forums is the tank swells some if it has had fuel in it and shrinks some if it has been sitting open. The other thing I've seen several times is folks reporting that a new pump (same size as the old one they took out) won't go back in.

The reason has been they set the tank on the sump and the top of the tank droops a bit. Better way is to leave the tank in the skid if the skid isn't damaged or set the tank on a couple of spacers under the end so the middle droops down a bit where the sump is.
 

SSTJ

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Yeah, that is more than a bit odd.

Nope, all TJ tanks are the same shape and external size give or take a few sixteenths of an inch.

What does happen and I've seen this in person and reported on the forums is the tank swells some if it has had fuel in it and shrinks some if it has been sitting open. The other thing I've seen several times is folks reporting that a new pump (same size as the old one they took out) won't go back in.

The reason has been they set the tank on the sump and the top of the tank droops a bit. Better way is to leave the tank in the skid if the skid isn't damaged or set the tank on a couple of spacers under the end so the middle droops down a bit where the sump is.

Interesting, thanks. But in this case, the pics show that the new unit was undeniably taller than the old one, right?

Here is the fourth pic he posted. Is this another quirk of the 97s?

Screen Shot 2022-01-14 at 09.43.13.png
 
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Tim_with_the_tj

Tim_with_the_tj

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Wow, nice work! Yes, definitely sounds like your gauge (sending unit) was off. Fixing that might have been the only thing you needed, whereas in my case the gauge was accurate. But of course you should now also be able to get a total of 19 gallons in there, from trimming the vent tube.

Good job hacking that pump assembly. I would probably have chickened out at that point.

I'm surprised that the 19-gallon Delphi was a different size. I wonder if it was for a later-model TJ, which might have a differently-shaped tank?
I appreciate your help especially on this. My vent tube was not sagging, for what it’s worth. I think the sending unit was just toast like @williambmac said. It looked even worse in person.

Here is the pump assembly I bought just for the record. If this was somehow the wrong part number then someone please let me know.
6653F053-C83F-458C-91AA-DB1AFFF93131.png

1FA2E96D-DC4E-49B3-9361-8F503B4ACF81.png

Yeah, that is more than a bit odd.

Nope, all TJ tanks are the same shape and external size give or take a few sixteenths of an inch.

What does happen and I've seen this in person and reported on the forums is the tank swells some if it has had fuel in it and shrinks some if it has been sitting open. The other thing I've seen several times is folks reporting that a new pump (same size as the old one they took out) won't go back in.

The reason has been they set the tank on the sump and the top of the tank droops a bit. Better way is to leave the tank in the skid if the skid isn't damaged or set the tank on a couple of spacers under the end so the middle droops down a bit where the sump is.
The skid has taken some hits in the past and is bent on the passenger rear. This might be distorting the tank slightly. It’s hard to say without removing the skid and really looking around. It does also appear that it’s possible someone may have rested the tank on top of something near the sump area like you said.

I say this because while measuring the distance from the bottom of the sump area to the top of the threaded lip (height of fuel pump assembly) I noticed the measurement was about 1/4” less at the rear of the tank. I don’t know if that’s normal or not. Regardless, the new pump assembly was roughly 3/8 too tall overall. It wouldn’t fully seat down into the tank seal.

While deciding what I could do and taking those measurement, I noticed that only cutting the new cage would not be enough to reduce the height of the whole assembly. It would still be too tall because the cage was not the only limiting factor. The pump was connected to the hat via a plastic tube with a spring. When fully compressed it was still too tall. Here’s what I’m talking about (minus the pump).



So ultimately I decided to cut down the cage to match the height of the old one and use the old hat with the new pump. This way I could connect the pump using the submersible flex hose and the assembly wouldn’t bottom out on itself like this one. I was also able to use the new sending unit/float with the new cage, which was important. These are the reasons why it didn’t fit and the reasons why it did once I was finished with it.

I hope this is helpful to someone. It would be simpler to buy a 15 gal pump assembly in this situation, but I wanted the 19 gal so that hopefully the gauge will read correctly after the vent tube mod. That is TBD.
 
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Tim_with_the_tj

Tim_with_the_tj

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@SSTJ Filled her up. Here’s what she held plus the ~6.5 gallons I put in at home.

F9BE760F-3732-438F-A990-F9648167D20A.jpeg

The gas station is about 7 miles from my house, so I’m gonna say total capacity is around ~18.5 gallons now. Win.

Here’s what the gauge reads.
843BE801-5A7B-4379-8268-06E24F0298B3.jpeg

Overall I’m happy with the results. It also fixed my hard starting issue after the Jeep sits for 15-30 mins or longer. Thanks to all who helped.
 
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aston4

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Are you sure you don't have a 15 gallon tank? There was a thread I read on here about someone modifying a 15 gallon tank to a 20 gallon by trimming a vent line... or something to that effect. They said the actual tanks were identical in dimensions, just the 15 gallon was mechanically limited.

Found it...
This

I've read that several times. 19 gallon tank was a dealer option $ and they just removed all that junk.

if i take about fifteen minutes and fill my 96 build VERY SLOWLY I can fit 19 gallons in my 15 gallon tank and I’ve been doing it for years. Haven’t gotten around to dropping the tank and cutting all that crap out.
 
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Tim_with_the_tj

Tim_with_the_tj

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This

I've read that several times. 19 gallon tank was a dealer option $ and they just removed all that junk.

if i take about fifteen minutes and fill my 96 build VERY SLOWLY I can fit 19 gallons in my 15 gallon tank and I’ve been doing it for years. Haven’t gotten around to dropping the tank and cutting all that crap out.
I knew I had the 15 gallon tank the whole time. The problems I experienced and the solutions are all in the thread. You should read it. Seems like you didn’t.